The present invention relates generally to engine exhaust gas noise suppression, and more particularly provides uniquely configured, compact apparatus, and associated methods, for cooling and attenuating the noise of exhaust gas discharged from a gas turbine engine.
With increasing frequency, gas turbine engines are being utilized in both stationary and mobile ground installations to perform a variety of functions such as generating electricity, providing a flow of compressed air, or furnishing mechanical power via a rotating shaft. In such ground installations, exhaust gas noise suppression apparatus typically must meet three performance criteria.
First, and perhaps foremost, the suppression apparatus must satisfactorily attenuate the engine noise associated with the hot, high velocity gas discharged from the engine. As is well known, such noise is of a fairly complex nature, being generated across varying frequency bands at different intensities, depending on the type and size of the particular engine. The primary noise components which must be attenuated are "core" and "turbine" noise.
Core noise is a low frequency noise component believed to be at least partly caused by the combustion processes within the engine, while turbine noise is a high frequency noise component caused by the interaction of high velocity gases within the engine's turbine section. The frequency spectrum of core noise is essentially broadband, peaking at a relatively low frequency around 200 to 800 Hz where most of the energy of such core noise is concentrated. Turbine noise, on the other hand, is a significantly higher frequency noise phenomenon, having both broadband and discrete spectral components, peaking at a relatively high frequency around 6,000 to 10,000 Hz.
The second performance criteria which often must be met is that the hot exhaust gas must be cooled before its discharge to atmosphere to protect operating or other personnel in the engine's vicinity from potential burn injuries. Additionally it is often desirable to generate (via the suppression apparatus) a cooling flow which serves not only to lower the ultimate discharge temperature of the exhaust gas, but also provides for cooling of miscellaneous equipment adjacent the engine and/or the noise suppression apparatus. The third performance criteria is that the particular noise suppression apparatus should not inordinately restrict the engine's exhaust gas flow.
Conventional apparatus utilized to cool and attenuate the noise of turbine engine exhaust gas typically must compromise between and among these three performance criteria. This previously necessary compromise is due to the high desirability of meeting the three criteria with suppression apparatus which fits within a suitably compact space envelope. For example, if a sufficient number of noise attenuating devices are positioned within the typical conventional exhaust gas sound attenuator to satisfactorily attenuate both the core and turbine noise components, the suppressor exits the realm of compactness, often approaching the size of the engine which it is designed to silence. On the other hand, if a suitable degree of compactness is achieved, other difficulties follow, such as a relatively high degree of gas flow restriction, insufficient noise reduction, and/or inability to adequately cool the exhaust gas flow prior to its discharge to atmosphere.
Accordingly, it is an object of the present invention to provide turbine engine exhaust gas noise suppression and cooling apparatus, and associated methods, which eliminates or minimizes above-mentioned and other problems typically associated with conventional apparatus and methods.